In a conventional displaying apparatus, for example, a decorative illumination signboard, a fluorescent light source and a light reflector are disposed underneath an opaque plate on which an advertising medium is printed to isotropically diffuse a light flux emitted from the light source.
In recent years, along with an appearance of tall buildings, so-called suburban restaurants, convenience stores, and gas stations, in order to improve visibility from far, a decorative illumination signboard which can be mounted on a high place of a building have been increased.
The decorative illumination signboard as mentioned above isotropically scatters the light flux so that the light flux is radiated in a direction toward the sky where no specifically intended person exists and therefore, energy is vainly wasted. Furthermore, the unnecessary light flux causes the night sky to be brightened up, and there is a problem of so-called light pollution.
Therefore, in Patent Document 1 mentioned below, a deflection sheet which has a prism and deflects the light radiated by the light source in a downward direction is proposed. In the deflection sheet in Patent Document 1, microscopic protrusions are provided on a non-significant surface of the prism in order to scatter the light which enters the non-significant surface and causes an upwardly emitting component so that the upwardly emitting component is reduced. However, it is assumed that producing a die or shaping so as to provide the microscopic protrusions on one of light controlling surfaces of the prism sheet is difficult.    Patent Document 1: Japanese Patent Application Publication No. 2000.193809